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tear out on inside of bowl bottoms

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tear out on inside of bowl bottoms

Postby Andyp » 15 Jun 2020, 10:20

What is you preferred method for reducing or preventing tear out on the inside of a flat bottomed bowl.

I suspect it is a combination of technique and tool. I only have bowl gauge and square scraper with a S shaped tool rest. Try as I might I always end up with small quadrant (about an 1/8th) of tear out towards the outside of the bottom (on the inside).
Sanding of course gets rid of this but should I be able to achieve zero tear out from the tool?
cheers

Andy
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Re: tear out on inside of bowl bottoms

Postby Woodbloke » 15 Jun 2020, 17:45

Andyp wrote:What is you preferred method for reducing or preventing tear out on the inside of a flat bottomed bowl.

I suspect it is a combination of technique and tool. I only have bowl gauge and square scraper with a S shaped tool rest. Try as I might I always end up with small quadrant (about an 1/8th) of tear out towards the outside of the bottom (on the inside).
Sanding of course gets rid of this but should I be able to achieve zero tear out from the tool?

Nope, you won't achieve a perfect finish straight from the tool; there will always be tool marks or tear out of some sort. When I was in NZ a while back a pro turner made me a superb bowl in very rare, green 'whitebait' ancient kauri (pronounced correctly by the Maori as 'kohri' not 'kowri' which is how the Aussies pronounce it) which you can see at the end of this clip
I asked him about finishing straight from the tool and he said that you always need to sand, it fact he power sanded up to about 400g and then used w/d papers to around 2000g :shock:

IMG_2082.jpg
(154.81 KiB)


I use the power sanding Kirjes system from Classic Hand Tools which is fantastic. I also use a Flexipad from the old firm with Abranet films, the caveat being that you must have a really good extraction system to cope with the dust - Rob
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Re: tear out on inside of bowl bottoms

Postby Dalboy » 15 Jun 2020, 20:30

Have you got a photo Andy. You should be able to get a good enough finish from the tool ideally a single motion from the rin to the centre with a freshly sharpened tool. It also helps to use the correct grind as some are better for a sharper transition from the wall to the base.
Wood type can also effect it as a soft punky wood will tear out no matter what you do
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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 07:01

Rob, I don’t think my budget could stretch to a Kirjes system. Do you use it with the bowl spinning on the lathe?
Maybe an alternative power sander would help
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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 07:13

Dalboy wrote:Have you got a photo Andy. You should be able to get a good enough finish from the tool ideally a single motion from the rin to the centre with a freshly sharpened tool. It also helps to use the correct grind as some are better for a sharper transition from the wall to the base.
Wood type can also effect it as a soft punky wood will tear out no matter what you do


No photo Derek, I did try and take one of the ash bowl I have on the lathe at the moment but i could not get a good enough image to show up the problem.

The current bowl is a bout 3” deep by 9 across with a flat bottom.
On the outside base of the bowl i can run the bowl gauge at the right angle to get what I consider an acceptable finish requiring just a little sanding*.
On the inside base of the bowl the sides of the bowl prevent the bowl gauge from being presenting at the same angle. I seem to be able to get an acceptable finish on the sides.

The tear out experienced is not across the whole inside just a small area where in my mind the gauge is cutting across end grain.

*It may well be that my idea of what is acceptable is too critical. How much tear out is acceptable?
cheers

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Re: tear out on inside of bowl bottoms

Postby Woodbloke » 16 Jun 2020, 17:10

Andyp wrote:Rob, I don’t think my budget could stretch to a Kirjes system. Do you use it with the bowl spinning on the lathe?
Maybe an alternative power sander would help

Yep, it's used with the bowl spinning on the lathe. You can use the pneumatic 'bulbs' in a power drill so you don't have to use the drive shaft/motor combo which makes it a bit more economical. The kit is quite expensive as it comes from Scandinavia, but in my experience, the cost is justified by the results and the abrasive loadings themselves seem to last quite a long time

Edit - ref acceptable 'tear out': none - Rob
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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 17:15

Thanks Rob,
I meant acceptable from the tool rather than after sanding.
cheers

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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 17:20

Here is the finished bowl.

IMG_20200616_175842125-1.jpg
(535.9 KiB)


IMG_20200616_175902331-1.jpg
(530.08 KiB)


IMG_20200616_180156233-1.jpg
(363.69 KiB)


I have 3 more pieces of that ash. I will try and remember to take images of any tear out I experience before I sand.
IMG_20200616_093437397.jpg
(270.44 KiB)


I would also like to see how much tear out you guys end up with straight from the tool.
cheers

Andy
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Re: tear out on inside of bowl bottoms

Postby Phil » 16 Jun 2020, 17:50

Nice looking bowl 8-) :eusa-clap:
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Re: tear out on inside of bowl bottoms

Postby Malc2098 » 16 Jun 2020, 18:00

Nice bowl. Could it be that ash's grain might be a bit more susceptible to tear out?
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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 18:36

Phil wrote:Nice looking bowl 8-) :eusa-clap:



Thanks Phil
cheers

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Re: tear out on inside of bowl bottoms

Postby Andyp » 16 Jun 2020, 18:40

Malc2098 wrote:Nice bowl. Could it be that ash's grain might be a bit more susceptible to tear out?


Thanks Malc, no it is not the ash which is beautiful to turn.
If you can put up with all the ads this article explains the problem quite well

https://turnawoodbowl.com/wood-bowl-tur ... le-secret/

I seem to manage the outside acceptably well. It is the inside, especially the bottom which causes the most problem.

I realise that I need to see first hand what other turners deem to be acceptable tear out from the tool.
cheers

Andy
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Re: tear out on inside of bowl bottoms

Postby Woodbloke » 16 Jun 2020, 23:11

I see from the pics that the bottom is flat (sorry, didn't cotton on to that from previous posts...doh!) That hard internal corner is going to cause a problem whichever way you slices it and I'm sure that even the Kirjes or Flexipad system would struggle with it. That internal corner is the sort of feature found in boxes and Jason Breach at Ax developed a set of tools to deal with it; not cheap though! :shock: - Rob
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